Water Quality

What is Phosphorus?

Phosphorus, or P, is a naturally occurring element and one of the three nutrients required by all forms of life. P is very important in our lake ecosystems because it is the limiting nutrient in them. In other words, there is naturally an abundance of potassium and nitrogen, so any extra P that is added to a lake is quickly used by the ecosystem to create new plant growth, like algae.

What is the main source of phosphorus?

Phosphorus occurs naturally in the environment. Most phosphorus in a lake comes from the soil, plants, animals and precipitation in and near the lake. But human development and activity can significantly contribute extra phosphorus to a lake. It’s this extra phosphorus that we can control and need to worry about.

The common sources of phosphorus, which can be controlled or influenced by community members:

Fertilizers: neither chemical nor natural fertilizers (manure) should be used near the lake or other water such as creeks, rivers and wetlands. These fertilizers contain phosphorus as one of their components; the phosphorus is what makes plants and grass grow!

Soaps and cleaners: many soaps and cleaners contain phosphorus (in phosphate form) as a binding agent. Look for phosphate-free cleaners, shampoo, and laundry detergent. Remember: never use TSP outside near the lake – the P stands for phosphorus!

Sewage (septic tanks): Maintain your septic system and remember to have your tank pumped out every 3 to 5 years. Replace it if necessary. If a new septic system is in your future, look for one that binds phosphorus. The best systems use special soils or have tertiary treatment technologies.

Stormwater and erosion: Make sure that your property has as little hard surface as possible, and maintain vegetation like trees, flowers and shrubs, especially near the shoreline. A 20m (66ft) vegetated buffer is recommended. If rainwater is able to infiltrate the soil, this allows plants to use the nutrients in rainwater before it enters the lake. Where possible direct run-off from hard surfaces away from the lake into rain gardens and soakway pits. The more infiltration that occurs, the better the chances are that phosphorous will not get to the lake.

Promote the preservation of wetlands and forest cover both on your property and in the community.

What is a phosphorus threshold?

Each lake in Muskoka has a calculated threshold associated with it. The threshold represents an unacceptable change in water quality for that lake. The threshold for each lake is defined as 50% higher than the historic P concentration before any human development. In other words, if a lake’s natural P concentration was 6 µg/L, the threshold is set at 9 µg/L. If human sources of phosphorus are seen to make a lake reach this threshold concentration, development regulations will be triggered, even if visible signs of a change in water quality aren’t seen.

How was the phosphorus threshold set and how do we know it is the right number?

Lake scientists have used computer models and observations to estimate what the phosphorus concentration in each lake was before human development. This is generally considered to be accurate, although the only way to definitively determine this background concentration would be to analyze a ‘core sample’ of the lake’s bottom. This would show the chemistry of the lake over several centuries.

In most cases, it is safe to assume that this estimated historical concentration is accurate. The threshold of 50% more than this historic concentration was chosen by lake scientists as being the most reasonable level of protection for lakes in Muskoka.

What actions can we take with ‘non-conforming’ (eg. old/no septic system) cottagers?

Talk to you neighbor, if you have a good relationship with them. You’d be surprised to know that many cottagers unfortunately don’t know about the basics of maintaining their system! Most people will want to do the right thing to protect the lake, and their health!

Another option is to file a complaint with your local municipality, especially if you can smell a septic system. While some systems are `grandfathered` and therefore are not subject to the same regulations as a new system would be today, the municipality usually has the ability to order homeowners to maintain their system under the Ontario Building Code.

How often should I have my septic tank pumped out?

You should have your septic tank pumped out at least once every five years, even if it is not full. Every 2-3 years is even better.

What type of plants should I plant on my shoreline?

Always try to plant native species. More specific information is available on the MLA website here, your local nursery or by contacting the MLA office.

Why would total coliforms & E.coli be up or down in a year?

The weather has a significant impact on bacteria because they more easily survive in certain conditions. Cooler temperatures will yield lower numbers, while rainy warm weather will yield higher numbers.

What do our bacteria readings tell us about swimming safety?

It is important to remember that bacteria are always present in surface water. This is why it is never safe to drink untreated surface water. But swimming is usually fine because there is a much smaller risk of ingesting bacteria that will make you sick.

Public Health Units carefully monitor E.Coli levels at public swimming beaches. If an average of samples is greater than 100 cfu, a public beach will be closed. Bacteria levels in our lakes, even at single sites, almost never reach these levels. Also remember that a single high result probably does not mean that there is bacterial contamination. If multiple adjacent sites have E.coli readings above 100 cfu/100mL, further action should be taken. In this case, contact the MLA office.

What are total coliforms (colony forming units)?

Total coliforms are a broad categorization of bacteria often found in nature. E.Coliis one type of coliform, indicative of fecal contamination.

Can the Muskoka watershed handle all the golf courses?

Most golf courses now have well educated superintendents that are proactive and practice Best Management Practices. This can be beneficial both to the environment and the course itself since fewer chemical fertilizers and pesticides mean fewer chemicals in the environment and lower operating costs. If new golf courses are developed properly, site plan controlled and have an effective monitoring program, golf courses could have a smaller impact than some other types of development. But as with any development, there will be some environmental impacts that must be managed carefully.

What influence does the flushing of the lake have on water quality?

When a lake's water is completely renewed (flushed) quickly, it is much less sensitive to phosphorus loading because phosphorus added to the lake basin will quickly be sent downstream and not settle into the sediment at the bottom of the lake. This is usually the case when larger rivers enter the lake and leave the lake. For example, the water in Lake Muskoka moves through the lake much faster than water in Lake Joseph even though it is much larger. Lakes with a high flushing rate are typically able support more development than a lake whose water is flushed slowly.

What causes colouration of lakes?

Most lakes in Muskoka are very clear because they have very few nutrients (P) in them but many factors can contribute to the colour of a lake. Dissolved organic carbon, usually found in lakes whose watershed is rich in peaty soils, is most often responsible for the `tea` colour of some lakes in Muskoka. Some lakes can appear green if they are biologically productive (that is, have higher nutrient levels).